1. Field of the Invention
This invention relates to fine polyurethane particles useful as powder coating compositions, powder coating agents, an additive for coating compositions or a modifier for resins, rubbers and elastomers; and also to a process for the production of the fine polyurethane particles.
In addition, this invention also relates to fine polyurethane gel particles which are useful as a modifier capable of imparting, to coating compositions, resins, rubbers, elastomers or the like, excellent properties such as oil absorbance, heat resistance and abrasion resistance; and also to a process for the production of the fine polyurethane gel particles.
This invention is also concerned with colloidal polyurea particles; and a production process thereof.
2. Description of the Related Art
Fine polyurethane particles have conventionally been used as powder coating compositions, powder molding compositions, additives for coating compositions and modifiers for resins, rubbers or elastomers.
On the other hand, a polyurethane gel is obtained by a three-dimensional reaction of a polyisocyanate with an active-hydrogen-containing compound and is excellent in solvent resistance, heat resistance, abrasion resistance and oil absorbance.
As a method for making use of such excellent properties of the polyurethane gel, it is conducted to blend a polyurethane raw material (polyisocyanate), which has not been gelated yet, in a coating composition, coating agent, molding resin, rubber or elastomer and after forming the resulting blend into a coating film or a molding, to complete its gelation.
The above method, however, is accompanied with such a drawback that the crosslinking density of the gel is hardly controllable and depending on the degree of crosslinking of the gel, the compatibility of the gel with a coating film or molding may be lowered or physical properties of the coating film or molding may conversely be deteriorated. The above method is therefore limited in its application range.
As a method for overcoming such a problem, it is also conducted to first prepare fine polyurethane gel particles and then to mix them in a coating material or a molding resin. Conventional production methods for fine polyurethane gel particles includes, for example, mechanical grinding of a solid polyurethane gel at low temperatures, precipitation of fine polyurethane gel particles from an aqueous emulsion and subsequent drying, spray drying, and addition of a bad solvent to a solution-polymerized polyurethane gel to precipitate the polyurethane gel in the form of fine particles, followed by collection by filtration and further by drying for the elimination of the solvent.
These conventional processes are however accompanied by the problems that the resulting fine polyurethane gel particles have irregular shapes and cannot be obtained as fine polyurethane gel particles. They also involve the additional problem that the production cost is considerably high.
On the other hand, processes making use of an inert liquid are also known, including those disclosed in U.S. Pat. No. 3,787,525 and Japanese Patent Applications Laid-Open (Kokai) Nos. HEI 2-4860, HEI 2-38453 and HEI 4-255755.
The above methods and/or processes are also used in exactly the same manner for the production of ungelated fine polyurethane particles
The former approaches are not considered practical for inferior productivity. The latter approaches, on the other hand, all require a special dispersion stabilizer, leading to the problem that a limitation is imposed on the combination of the composition of the polyurethane or polyurethane gel as a dispersoid and the dispersion stabilizer. The latter approaches are also accompanied with such drawbacks that the composition of the polyurethane or polyurethane gel so synthesized is limited to a narrow range, that the particle size of the fine polyurethane particles or fine polyurethane gel particles cannot be controlled easily and that upon collection of the fine polyurethane particles or fine polyurethane gel particles from the dispersion, the particles tend to stick together into coarser particles.